- Heat pumps
- Air-to-water heat pump
H91
Panasonic H91 on an Aquarea heat pump: tank heater cut-out
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
Medium
Quick answer
On an Aquarea, H91 means the thermal protection of the hot water tank's electric immersion heater has tripped. Check the cylinder thermostat is not set too high, reset the error and call the installer if it comes back.
Safety first
Stop and check this first
- Panasonic's guide warns that domestic hot water stored above 60 ºC can scald: take care when opening a hot tap after a heating cycle.
- The tank immersion heater runs at mains voltage: do not open its cover or touch the limit stat; that check belongs to a qualified installer.
Safe checks you can perform
- Look at the cylinder thermostat
- Reset the error and watch when it returns
- Check whether hot water still comes through
Leave these tasks to a qualified professional
- Do not attempt this professional task: Check of the tank heater limit stat
- Do not attempt this professional task: Check of the Tank Heater setting and connector CN6
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Check of the tank heater limit stat
What they doThe installer checks whether the immersion heater's high limit stat has tripped, resets it and looks for why it tripped, as Panasonic's flowchart says.
They must show youthe state of the limit stat and the cause found for the trip.
In writingthe cause of the trip, whether the stat was reset or replaced and why.
Check of the Tank Heater setting and connector CN6
What they doThe technician checks whether the tank heater is configured as internal or external and, if external, that the limit stat or link is properly connected at CN6 on the main board.
They must show youthe Tank Heater setting on the controller and the CN6 connection.
In writingthe final configuration, any wiring changes and the test with the heater running.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Look at the cylinder thermostat
- Who:
- you, without opening electrical covers.
- How:
- if your cylinder has a thermostat you can adjust from outside, check its setting. Panasonic asks you to make sure it is not set too high before resetting H91. Do not remove covers to reach it.
- Result that matters:
- knowing whether the cylinder was set higher than needed.
- If it was very high:
- turn it down to a sensible value or ask the installer for the correct setting.
- If the setting is normal or not accessible:
- reset the error and watch.
- Evidence to keep:
- photo of the thermostat and its setting.
Evidence: Panasonic Aquarea user guide for Bi-Bloc, Monobloc and All in One, C, D and E series
Reset the error and watch when it returns
- Who:
- you, on the heat pump controller.
- How:
- reset the error as your Aquarea guide describes. Notice whether and when it comes back: the error only appears when the tank heater switches on, for example during hot water heating or legionella cycles.
- Result that matters:
- knowing whether H91 was a one-off or repeats with the heater running.
- If it does not return:
- note the date and watch the next hot water cycles.
- If it appears again:
- contact the installer quoting the code, as Panasonic asks.
- Evidence to keep:
- note of the dates and times H91 appears.
Evidence: Panasonic Aquarea user guide for Bi-Bloc, Monobloc and All in One, C, D and E series · Panasonic Aquarea installation guide 1.2, Monobloc solutions H and J generation
Check whether hot water still comes through
- Who:
- you.
- How:
- open a hot tap and notice whether the temperature is normal. That tells you whether the cylinder is still being heated by the heat pump while the immersion heater is locked out, which is useful to tell the installer.
- Result that matters:
- a sense of the real impact of the error on your hot water.
- If the water is hot:
- the alert is not extremely urgent, but the installer should check it.
- If the water is cold or lukewarm:
- tell the installer so the visit is prioritised.
- Evidence to keep:
- note of the perceived temperature and the time.
Evidence: Panasonic Aquarea user guide for Bi-Bloc, Monobloc and All in One, C, D and E series
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Heat pumps
- Brand
- Panasonic
- Product type
- Air-to-water heat pump
Known code variants
- Aquarea H91
- Aquarea immersion heater H91
- Aquarea resistencia del depósito H91
- Aquarea tank heater OLP H91
- Aquarea termostato acumulador H91
- bomba de calor Panasonic H91 agua caliente
- error H91 aerotermia Panasonic
- H91
- Panasonic Aquarea H91
- Panasonic heat pump error H91
- Panasonic heat pump H91 hot water
What it means
In the Aquarea C, D and E user guide, H91 is the overload protection (OLP) of the hot water tank immersion heater. The Monobloc H and J installation guide explains that, with the tank heater set to External, the unit errors if that heater's limit stat goes open circuit, and that it only appears when the heater is actually activated. Panasonic asks you to check the cylinder thermostat, reset and call if it returns. The code does not prove the immersion heater is faulty.
Warnings and stop conditions
- Mediumeditorial warning
Panasonic's guide warns that domestic hot water stored above 60 ºC can scald: take care when opening a hot tap after a heating cycle.
Evidence: Panasonic Aquarea user guide for Bi-Bloc, Monobloc and All in One, C, D and E series
- Highsource verified
The tank immersion heater runs at mains voltage: do not open its cover or touch the limit stat; that check belongs to a qualified installer.
Evidence: Panasonic Aquarea user guide for Bi-Bloc, Monobloc and All in One, C, D and E series · Panasonic Aquarea installation guide 1.2, Monobloc solutions H and J generation
Symptoms and causes
Probable causes · in order
- Cylinder thermostat set too highCommon
This is the first thing the user guide asks you to check: a very high thermostat can take the water to the point where the limit stat acts.
Evidence: Panasonic Aquarea user guide for Bi-Bloc, Monobloc and All in One, C, D and E series
- Immersion heater safety limit stat trippedCommon
The installation guide likens the OLP to a high limit for the tank booster heater: if it opens, the unit shows H91.
Evidence: Panasonic Aquarea installation guide 1.2, Monobloc solutions H and J generation
- Tank heater setting or CN6 connectionPossible
With Tank Heater set to External, the link or the limit stat on connector CN6 of the main board is missing; Panasonic's flowchart covers this.
Evidence: Panasonic Aquarea installation guide 1.2, Monobloc solutions H and J generation
Virtual technician
Does H91 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
Panasonic Aquarea user guide for Bi-Bloc, Monobloc and All in One, C, D and E series
Panasonic · 2014 · manual
- 2
Panasonic Aquarea installation guide 1.2, Monobloc solutions H and J generation
Panasonic · 2021 · manual
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